OBJECTIVE: To monitor the effectiveness of the prevention of mother-to-child transmission (PMTCT) components in reducing mother-to-child transmission of HIV in Kilimanjaro region, Tanzania. METHODS: We conducted a retrospective registry-based cohort study of HIV-exposed children aged 4 weeks to 18 months. Eligible children had a DNA polymerase chain reaction HIV antigen test between January 2009 and August 2012. We collected and analysed the data on the PMTCT components provided. We used logistic regression to explore factors associated with successful PMTCT usage and with infant infection. RESULTS: We studied 561 children; 283 (50.5%) were from rural areas. Breastfeeding was reported by 519 (92.5%) of mothers. In 469 (83.6%) mother-baby pairs, both received chemoprophylaxis, whereas in 9 (1.6%) pairs, neither mother nor baby received any chemoprophylaxis. Of the 522 (93.0%) infants with known outcomes at 6 months, 227 (43.5%) were alive, 258 (49.4%) were lost to follow-up, 34 (6.5%) had transferred and 3 (0.6%) had died. A total of 54 (9.6%) children were infected. Transmission rates of HIV when only the mother (adjusted odds ratio [aOR] 1.49, 95% CI: 0.47-4.77) or only the baby (aOR 1.06, 95% CI: 0.23-5.01) received chemoprophylaxis were not significantly different from transmission rates when both mother and baby received antiretroviral chemoprophylaxis. Mixed feeding practices were not associated with significantly increased risk (aOR 4.09, 95% CI: 0.58-28.76) compared with exclusive breastfeeding. CONCLUSION: This study showed that rate of MTCT of HIV was 9.6% in Tanzania between 2009 and 2012. The intrapartum and child chemoprophylaxis components of the PMTCT programme were well implemented with 84% of both mothers and their babies getting full chemoprophylaxis, and effective in reducing mother-to-child transmission.